1. Field of the Invention
This invention relates to an illuminating apparatus and a projector, which is suitable, for example, for a liquid crystal projector for enlarging and projecting an image displayed on a liquid crystal display device onto a screen by a projection lens.
2. Related Background Art
Recently, a liquid crystal projector for enlarging and projecting an image displayed on a liquid crystal display device onto a screen by a projection lens is known as a large dynamic image display apparatus. In such a liquid crystal projector, it is a technical task to increase the illuminance on the screen, and for this purpose, a microlens is disposed on each liquid crystal pixel to thereby increase the numerical aperture of each pixel.
FIG. 1 of the accompanying drawings is a schematic view of the essential portions of a single plate type liquid crystal projector disclosed in Japanese Laid-Open Patent Application No. 4-60538. In FIG. 1, the reference numeral 101 designates a white light source, and the reference numeral 102 denotes a spherical mirror, of which the center of curvature lies at the position of the white light source 101. The reference numeral 103 designates a condenser lens, of which the forward focus lies at the position of the white light source 101. The reference characters 104R, 104G and 104B denote dicroic mirrors having the characteristic of selectively reflecting lights of the red, green and blue wavelength zones and transmitting other two wavelength zones therethrough. The reflecting surfaces of the three dichroic mirrors are not all parallel to one another, but are designed such that an incident light becomes three rays of light slightly different in angle after the lights of respective wavelength zones are reflected by the three mirrors. The reference numeral 120 designates a transmission type liquid crystal display device, and a microlens array 110 is attached to the light incidence side thereof. The reference numeral 105 denotes a field lens, the reference numeral 106 designates a projection lens for enlarging and projecting an image displayed on a liquid crystal display element 120, and the reference numeral 107 denotes a screen.
The action of this example of the prior art will now be described. Light emitted by the white light source 101 is made into a substantially parallel light beam by the condenser lens 103 and enters the group of dichroic mirrors. First, the dichroic mirror 104R reflects red light in the white light and transmits the remainder therethrough. Then, the dichoroic mirror 104G reflects green light in the remaining light. Then, the dichroic mirror 104B reflects the remaining blue light. Accordingly, the white light is reflected by the group of dichroic mirrors and becomes red light, green light and blue light different in direction and thereafter travels toward the liquid crystal display element 120.
FIG. 2 of the accompanying drawings is an illustration of the action near the liquid crystal display element of FIG. 1. In FIG. 2, the reference numeral 122 designates the scanning electrode of the liquid crystal display element, and the reference characters 121B, 121G and 121R denote the signal electrodes of a blue pixel, a green pixel and a red pixel, respectively. By exciting each signal electrode, the pixel in the portion of the signal electrode can be controlled. A set of R, G and B pixels corresponds to a single microlens.
In this case, red illuminating light entering a microlens is condensed on the portion of the R pixel corresponding to this microlens, and green illuminating light and blue illuminating light entering the microlens are likewise condensed on the portions of the G pixel and the B pixel, respectively, corresponding to the microlens. Thereby, with the white light source as a light source, the R, G and B pixels of the single plate liquid crystal display element are illuminated with the red illuminating light (R), the green illuminating light (G) and the blue illuminating light (B), respectively, without the use of color filters.
Turning back to FIG. 1, the image displayed on the liquid crystal display element is made into a color image by the above-described action, and is enlarged and projected onto the screen 107 by the field lens 105 and the projection lens 106.
According to the construction of this example of the prior art, the absorption loss by each color filter becomes null and therefore, it is possible to increase the illuminance on the screen to the level of a three-plate type projector.
FIG. 3 of the accompanying drawings is an illustration of the task of the single plate type liquid crystal display device of FIG. 1 showing the arrangement of the red (R), green (G) and blue (B) pixels. R, G and B represent pixels for red, green and blue, respectively, and for example, red light reflected by a red reflecting dichroic mirror in a color resolving system enters the pixel R for red, green light reflected by a green reflecting dichroic mirror enters the pixel G for green, and blue light reflected by a blue reflecting dichroic mirror enters the pixel B for blue.
The red illuminating light resolved by the color resolving system and entering the liquid crystal display device is imaged on the liquid crystal display device with a width RL indicated in FIG. 3 by the microlens formed on the aforedescribed pixel.
Assuming that the light emergence side of an illuminating apparatus (101-103 in FIG. 1) for illuminating the liquid crystal display device is not telecentric relative to white light and there is a difference in the angle of incidence of the red illuminating ray of light between the center and corners of the display surface of the liquid crystal display device, even if with regard to the pixel R for red at the center of the display surface, the width RL depicted by a dotted line can be adjusted so as to be within the R pixel, the red illuminating light entering the pixels in the peripheral portion of the display surface is imaged while deviating relative to the center of the pixel as indicated by dots-and-dash line in FIG. 1. In this case, with regard to the R pixels in the peripheral portion of the liquid crystal display device, the loss of the quantity of light occurs and further, a phenomenon such as the color irregularity of the peripheral portion due to the fact that the red illuminating light which originally should enter the R pixel enters the G pixel to be displayed by green occurs and the quality of image is reduced.
It is the object of the present invention to provide an illuminating apparatus and a projector which are good in telecentric characteristic with respect to white light.
A first aspect of the present invention is an illuminating apparatus of which the light emergence side is telecentric and a projector having the same, and in which an optical system for applying white light from a light source to a surface to be illuminated is provided with a first lens having positive refractive power and a second lens having negative refractive power, the first lens and the second lens differing in Abbe""s number from each other.
A second aspect of the present invention is an illuminating apparatus of which the light emergence side is telecentric and a projector having the same, and which have a light condensing optical system for condensing white light from a light source on a surface to be illuminated and a directing optical system for directing the white light from the light source to the condensing optical system, the directing optical system having a relay lens provided with a lens having positive refractive power and a lens having negative refractive power, the positive and negative lenses differing in Abbe""s number from each other.
A third aspect of the present invention is an illuminating apparatus of which the light emergence side is telecentric and a projector having the same, and which have an optical integrator, a directing optical system for directing white light from a light source to the optical integrator, a condenser lens for condensing the light from the optical integrator on a surface to be illuminated, color resolving means for resolving the white light from the condenser lens into red, green and blue lights and causing the red light, the green light and the blue light to enter the surface to be illuminated from different directions, and a relay lens for relaying the light from the integrator to the condenser lens, the relay lens being provided with a lens having positive refractive power and a lens having negative refractive power, the positive and negative lenses differing in Abbe""s number from each other.